Squid-Based Traffic Control and Management System
Internet access is one of the major and most demanded services in the computer network of any organization. Olifer and Olifer, in Computer Networks: Principles, Technologies and Protocols write that during the past 10–15 years, the 80/20 split between internal and outgoing traffic has turned over, and the split is now 80% outgoing (see the on-line Resources). The speed of access, the number of services and the volume of available content increase permanently. And the actuality of the Internet user access control task grows up. This problem is quite old, but now some of its aspects are changing. In this article, we consider the variants of its modern solution in the example of the computer network at Bashkir State Pedagogical University (BSPU).
First, we proposed some initial requirements for the Internet access control and management system:
User account support and management.
User traffic accounting and control.
Three types of user traffic limitation: per month, per week and per day.
Support for mobile users—people who use different computers each time they access the Internet, such as students.
Daily and weekly statistics and system condition Web and e-mail reports.
Web-based statistics and system management.
Apparently, these requirements do not specify the system implementation stage in any way and hence do not limit our “fantasy” in this aspect. Therefore, we have done a general consideration of the problem and how to solve it. In the rest of this article, we discuss the ideas and reasoning that led us to our final decision.
Let us revisit the Internet access process itself, with the example of the most popular World Wide Web (WWW) service:
The user runs the browser and enters the required URL.
The browser establishes the connection either directly with the WWW server via the gateway, which makes the network address translation or other network packet manipulations, or with the proxy server, which analyses the client request thoroughly and looks through its cache for the required information. If there is no such information or if it is outdated, the proxy server connects with the WWW server in its own name.
The obtained information is returned to the client.
The browser ends the connection or enters the keep-alive state.
Figure 1 shows the scheme of Internet user access organization.
The main elements of the scheme are the user; client software, including browser and operating system; workstation and other client hardware; network equipment; and the gateway (or proxy server). Other user authorization servers, such as Microsoft Windows domain controllers, OpenLDAP or NIS also may exist in the network.
As Figure 1 shows, the relation between the users and the workstations can be of the one-to-one or the many-to-many type. For instance, members of the university staff are mostly equipped with their own computers.
The main aspects of the problem are user traffic accounting, user authentication, user access control and management and reporting.
These aspects are quite independent of one another and each of them has several ways of implementation. The functions of authentication, traffic accounting and access control may be assigned to any element of the scheme above. And, the best solution will concentrate all of the functions in the single module or in the single access scheme element.
Access control can be implemented on the client side or on the server side. Client-side access control requires using the special client software, which also can authenticate the users. And, there are two ways of server-side access control implementation: firewall and proxy server. Firewall access control has the problem of user authentication. The network packets include only the IP addresses, which are not bound to user names. In the case of using a firewall, this problem has two solutions: use of VPN, which has its own user authentication mechanism and dynamic user-to-IP assignment control. This is possible with some external tools.
The simpler solution, however, is the use of the proxy server, which supports user authentication using the browser. There are three methods of browser authentication:
Basic authentication—a simple and widely distributed scheme, which is supported by the majority of Internet browsers and proxy servers. Its main disadvantage is that the user password is sent over the network with no encryption.
Digest authentication is a more reliable scheme, which uses password hashes for security. Its main imperfection is the lack of special software support.
NTLM authentication is specific for the Microsoft product network infrastructure. Nevertheless, this authentication scheme is acceptable and, furthermore, desirable in many computer networks, including Windows workstations, which are prevalent in Russia as far as we know. The main advantage here is the possibility of the integration of the proxy authentication scheme with Windows and Samba domain controllers.
The task analysis and some of the ideas above led us to the development of two systems:
VPN using PPTP based on the firewall internal features. Historically, the VPN server used FreeBSD, hence, we used the ipfw firewall interface and mpd ported application as a PPTP server. Traffic control is made using the free, distributable NetAMS system.
Squid-based Internet user access control and management system.
The first system was developed by Vladimir Kozlov and is used to connect the university staff members, who use dedicated computers for Internet access. Its main disadvantage is the requirement of a client-side VPN setup. This is a considerable obstacle in the case when the computer network is distributed and the users are not familiar enough with computers.
The second system was developed by Tagir Bakirov and is used to connect the majority of university users, who have no constant computer for Internet access. The complexity of the development was the main drawback of this solution. Next, we discuss the implementation of the second solution in detail.
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